11 NCERT PHYSICS SUBJECTIVE QUESTION

ch no 1 nahi hai or baki sb line say hai. ch no 1 is missed and all chapter is contineus form and 

Q1. What is Doppler's effect in sound waves?  Give an example.  What is the cause of Doppler's effect? Solution When a source of sound is approaching or is being approached by an observer, the pitch of the sound appears to be higher than its normal, and when it is receding or being receded by the observer, the pitch of the sound appears to fall below the normal.  This apparent change in the pitch due to the relative motion between the source and the observer (and the medium) is called Doppler's effect. When a whistling engine approaches an observer who is standing on the platform, he notices a rise in pitch, and fall in pitch when the engine recedes from him. It can be explained as follows.  When the whistling engine is approaching, the engine is following the waves already sent to the observer.  This results in crowding up of the waves.  The waves reach the observer in quicker succession and the pitch or the frequency, therefore, appears to rise....

Q1. What are coupled oscillations? Solution A system of two bodies connected by a spring so that both can oscillate in a straight line along the length of the string is known as a coupled oscillator.  The oscillations produced by a coupled oscillator are called coupled oscillations. Q2. Why are soldiers ordered to move out of step while crossing a bridge? Solution Every oscillator has its own frequency of oscillation.  When frequency of external force becomes equal to natural frequency of oscillations, resonance takes place and amplitude of vibration becomes maximum.  Bridge can be considered as stretched string.  If soldiers march in steps and frequency of marching steps is the same as that of frequency of bridge, then bridge will be set into resonant vibrations and hence collapse.  That is why soldiers are asked to break their steps. Q3. How earthquakes some times cause disaster? Solution When the waves produced during earthquake have...

Q1. What is meant by the term ' Molar specific heat ' of a gas?  The molar specific heat of hydrogen in the temperature range of about 250 K to 750 K is about (5/2) R.  At lower temperatures the value of molar specific heat of hydrogen decreases to the value typical of monoatomic gases (3/2) R while at higher temperatures, it tends to the value (7/2) R.  Explain. Solution Molar specific heat capacity of a gas refers to the amount of energy required for 1 mole of a substance to raise its temperature by 1 K.  In the temperature beyond 70 kelvin, rotational motion of H 2 gas starts.  So at 250 K < T < 750, the number of degrees of freedom becomes five -2 rotational and 3 translational Therefore,  C v =f/2 R becomes, C v = 5/2 R.  For lower temperatures only translational degrees of freedom will exist and no rotational freedom. Therefore,  C v = 3/2 R. Q2. What do you mean by an ideal gas? Solution An ideal gas or a perfect ga...

Q1. Discuss the application of the first law of thermodynamics to Isothermal process. Solution Isothermal process :  Since temperature remains constant in an isothermal process, dU = 0 From the first law of thermodynamics, dQ = dU + dW Therefore, dQ = dW = PdV (a)  Therefore, if a gas is to expand isothermally, then an amount of heat equivalent to the work done by the gas will have to be supplied to it from the external source. (b)  During isothermal compression, dV will be negative.  This implies that during an isothermal compression, the amount of heat equivalent to the work done on the gas will have to be removed from it. (c)  During isothermal compression or expansion, there is no change in the internal energy of the gas.   Q2. What thermodynamic variable is defined by (a)  Zeroth Law? (b)  First Law? Solution (a) The thermodynamic variable defined by the zeroth law is temperature. (b) The thermodynamic variable ...

Q1. One thermometer is placed half metre above the tip of the fire and one thermometer is placed half metre at the side of the fire. Would the readings of the two thermometers be same or different and why? Solution The thermometer above the fire would show higher temperature as compared to the thermometer placed at the side of the fire because above the fire, heat is received due to radiation as well as convection whereas at the side of fire, heat is received only due to radiation. Q2. Define triple point of water. Why is it unique? Solution It is the temperature at which the three phases of water, namely, ice, liquid water and water vapour are equally stable and coexistent. The triple point is suitable because it is unique, i.e., it occurs at one single temperature = 273.15 K and one single pressure of about 0.46 cm of the Hg column. This point is unique because any temperature or pressure higher or lower will change the phase of one or more states of water. Q3. W...

Q1. If mustard oil and water are dropped out from a tube separately, the mustard oil comes out later than water. Why? Solution If mustard oil and water are dropped out from a tube separately, the mustard oil comes out later than water because the coefficient of viscosity of mustard oil is very large as compared to the coefficient of viscosity of water. Hence, water rushes out quickly than mustard oil. Q2. What is the weight of the body, when it falls with terminal velocity through a viscous medium? Solution When a body falling through a viscous medium attains terminal velocity, the apparent weight of the body is balanced by the viscous force due to the medium. Therefore, the weight of a body falling with terminal velocity is zero. Q3. Bernoulli's theorem is a consequence of which principle? Solution Bernoulli's theorem is a consequence of the principle of conservation of energy applied to fluids in a motion. Q4. A plane is in level flight at const...

Q1. What is a perfectly plastic body? Solution A body that does not tend to regain its original configuration on the removal of the deforming force is called a perfectly plastic body. Q2. What do you mean by the elastic limit? Solution When the deforming force is increased, a limit is reached beyond which if the applied force is removed, the solid does not come back to its original shape or size but remains deformed. This limit is called the elastic limit. Q3. What do you mean by stress?  Is it scalar or vector? Solution The restoring force developed per unit area of a deformed body is called stress.  It is a vector physical quantity. Q4. Which is more elastic, steel or rubber? why? Solution Steel is more elastic than rubber, because the inter-atomic bonding strength is more in steel than that in rubber. Q5. (a)  Which is more elastic:  rubber or glass? Why? (b)  Identical springs of steel and copper are equally stretched...

Q1. Can gravitational potential energy be 0. If yes how? Solution Yes, gravitational potential energy can be 0 when there is an infinite separation between the two interacting bodies. Q2. G is called Universal Gravitation Constant. Why? Solution G is called Universal Gravitation Constant because its value i.e. 6.67 x 10 -11 Nm 2 kg -2 is constant thought the universe. Q3. Does a pendulum vibrate in an artificial satellite? Solution No a pendulum doesn't vibrate in an artificial satellite as there is no gravity. The value of g = 0. Q4. Name a polar satellite. State its uses. Solution Sea star is a polar satellite. Polar satellites are used for 1.      Getting cloud images, 2.      Atmospheric data, 3.      To detect the ozone hole. Q5. In a gravitational field there is a point A where the gravitational potential is 0. Will the gravitational energy be 0? Solution In ...

Q1. What is the purpose of attaching a flywheel on a space craft? Solution A flywheel is attached on a space craft for controlling the orientation of the space craft. When neither the flywheel nor the space craft is turning then the total angular momentum is zero. To change the orientation of the spacecraft, the flywheel is made to rotate. The spacecraft starts rotating in the opposite sense to maintain the angular momentum of the system zero.When the flywheel is brought to rest, the space craft also stops rotating.But the orientation of space craft changes.  Q2. Convex and concave lenses of same mass and radius rotate about an axis passing through their centre and perpendicular to the plane. Which one will have greater moment of inertia? Solution The concave lens is thin at the centre and thick at the edges. As, more mass is concentrated away from the axis of rotation in case of concave lens, it will have more moment of inertia. Q3. What is the physical signif...

Q1. What do you mean by collision? Solution A collision between two bodies is said to have taken place when the two bodies physically touch each other. This short lived mutual interaction results into the change in energy and momentum of the interacting bodies. Q2. What do you understand by plastic collision? Solution A collision between two bodies in which two bodies stick together after collision and then move as one body, is called perfectly inelastic collision or plastic collision. In this type of interaction, momentum of the system remains conserved and loss of kinetic energy is maximum. Q3. 250 joules were spent in lifting a 10 kg weight to a height of 2 m. Calculate the acceleration with which it was raised. (Take g = 10 m/s 2 ) Solution Work done in lifting the weight = 250 J Work done against the gravitational force = m(g + a)h 250 = 10 x (10 + a) x 2 10 + a = 12.5 a = 2.5 m/s 2 Q4. What is the source of the kinetic energy of the falling rain...